Monolithic point-attack bit

ABSTRACT

A rotatable point-attack bit retained for rotation in a block bore, and used for impacting, fragmenting and removing material from a mine wall. An improved elongated tool body having at the front end a monolithic diamond-coated tungsten carbide wear tip that is rotationally symmetric about its longitudinal axis and contiguous with its protective tungsten carbide body, which is contiguous with a second section steel shank at the rear end. The two distinct parts are joined by a high impact resistant braze at ratios that prevent tool breakage.  
     The method of making such a monolithic section comprises of placing within a reaction cell the diamond powder and the carbide substrate and simultaneously subjecting the cell and the contents thereof to temperature and pressure at which the diamond particles are stable and form a uniform polycrystalline diamond surface on the tip of the carbide substrate thus forming a monolithic insert providing both cutting edge and steel body protection for increased durability and extended cutting tool life.

BACKGROUND OF THE INVENTION

[0001] The invention is directed to a rotatable cutting tool having a diamond tipped cemented carbide elongated protective body and a second steel body segment. The design of the invention is to provide improved performance and safety characteristics. These characteristics include a longer performance cycle through increased wear and fracture resistance resulting in a more efficient continuously penetrating material removal cycle and an improvement in safety, due to a monolithic diamond tipped carbide segment, that results in less chance for methane gas ignition and explosion. The protective large hard carbide section that has a high temperature and high pressure bonded diamond coated tip not only results in increased wear life of the bit body but also serves to protect the lower steel shank in tougher milling conditions.

[0002] Examples of rotatable cutting tools are on applications with long wall miners, continuous miners, and road planers. A longwall mining machine is used for mining coal seems underground. The machine includes two rotating drums having a plurality of blocks affixed thereto. Long wall mining tools typically comprise an elongated steel body with a hard cemented carbide tip brazed into a socket contained in the forward end of the steel body. One such point attack bit is described in U.S. Pat. No. 4,065,185. Attempts to improve performance have been made by hardening the insert tips of mining attack tools by the use of diamond compacts. One such diamond compact for use in cutting, machining, drilling and like operations is disclosed in Hall et al U.S. Pat. No. 4,604,106. Mining bits incorporating the diamond tips brazed onto steel inserts and subsequently brazed into steel bodies are shown in Anderson et al U.S. Pat. Nos. 5,837,071 and 6,051,079.

[0003] During the milling operation, the drums rotate so as to cause the rotatable cutting tools to impact the mine wall surface. The tools impact and fracture the wall surface. The surface fragments of coal chunks and powder are collected by a continuously moving conveyor belt and carried to the surface of the mine for processing. During the rotation of a drum, each rotatable cutting tool rotates about its central longitudinal axis. It is important that the tools continue to rotate because without adequate rotation a conventional tool will be locked into position and start an uneven wear pattern that leads to rapid tool degradation and ultimate tool failure. Due to the higher wear resistance of the protective monolithic cemented carbide body segment of the present invention, if the tool fails to rotate, the uneven wear pattern shown by conventional tools is greatly diminished or not noticeable when the tool clears and resumes its rotation.

[0004] The steel cutting tool body includes a reduced diameter portion adjacent to the rearward end thereof. A retainer is adjacent the reduced diameter portion of the steel body. The retainer functions to rotatably retain the rotatable cutting tool within the bore of the mounting block during the milling operation. Each block contains a central bore therein. This and other resilient retainer means useful with the present invention are described in U.S. Pat. Nos. 3,519,309 and 4,201,421.

[0005] A common mode of failure of polycrystalline diamond compacts, is the delamination of the diamond from the metal carbide substrate. Different attempts have been made to find a true bond that would resist delamination under the severe conditions employed. U.S. Pat. No. 5,011,515 discusses numerous attempts by previous inventors to solve the problem of delamination of the diamond layer from the carbide substrate. U.S. Pat. Nos. 4,592,433 and 4,784,023 teach parallel grooving of substrates to form ridges for increased bonding. U.S. Pat. No. 6,029,760 teaches the use of rounded cylindrical posts as support for diamond surfaces in rock drilling and machining wear resistant materials. These designs actually produce higher stresses in some portions of the cutter than that exhibited in the planar interface mounted PCD to carbide. However, all of the previous patents refer to rock and oil drilling or machining of parts where the stresses are not the same as for the application of this invention. This invention specifically addresses the use of diamond-coated picks, usually mounted on a rotating drum, for road pavement removal and recycling and coal mining, such as for continuous and long wall mining machines. A feature of this invention are the rounded radiused protuberances located at the tip of the carbide substrate, that serve to decrease the load stress concentrations and distribute them evenly over the surface, thus minimizing the potential for diamond delamination.

[0006] Other features of this invention are provided by a method for making a monolithic section, which method comprises the placing within a reaction cell pre-pressed forms of diamond particles affixed to the tip of the carbide substrate and simultaneously subjecting the cell and the contents thereof to temperature and pressure conditions at which the diamond particles solidify and are permanently reaction bonded to the cemented carbide substrate. The methods of making polycrystalline diamond in a high temperature, high-pressure press are well known in the art and further detailed description thereof is not considered necessary.

[0007] Another method of failure of previous inventions that use a small carbide, or diamond coated carbide tip bonded to a steel shank is braze failure at the carbide tip to steel shank junction, where the severe application forces exceed the tensile strength of the braze alloy causing bond failure of the small contact area between two dissimilar metals. This invention having a diamond tipped monolithic, longer extended carbide portion, makes the surface area where the carbide post is brazed to the steel shank of much larger diameter than previous inventions and further increases the surface area with a continuously varying radius that matches the profile of the steel shank pocket where it is bonded by a medium to high impact resistant braze. The larger brazed surface area ensures that the braze joint will not fail under most severe loading conditions, thus extending the life of the bit and contributing to safety by minimizing catastrophic tool failure.

[0008] Another method of failure is due to using diamond coated carbide tips limited in size as compared to the size of the diamond tip of the present invention. Having only a limited size carbide or diamond coated carbide tip results in bit failure when the steel holding the carbide or diamond coated insert is eroded away during application, exposing the cutting insert and allowing fracture thereof followed by catastrophic failure of the bit. In addition to the much larger protective surface area, the profile of the monolithic section is so designed as to guide the cuttings away from the ferrous shank preventing erosion of the steel body below the carbide section, thus significantly extending the life of the tool.

[0009] The present invention reduces the potential of sparking and explosion from ignition of methane gas. The ignition of methane gas, which is released from pockets where the gas has been trapped in the material being mined, is a safety problem. The causes of ignition are believed to be due to the heat generated through friction as the bits move through the coal and rock during the mining operation or due to sparking, which may occur when the steel base portions of the bits strike rock. Since the coefficients of friction of diamond and tungsten carbide are substantially lower than that of steel, less heat is generated as the monolithic body of the present invention cuts through coal and rock, thus reducing the possibility of gas ignition.

[0010] The protective monolithic body is preferably formed as a unitary member of cemented carbide or other material, which provides suitable hardness and abrasion resistance characteristics, and which at the top provides a diamond insert and at the bottom a radiused projection to allow inserting and brazing into a steel shank. The term “cemented carbide” refers to the type of material resulting when grains of carbide of the group IVB, VB, or VIB metals are pressed and sintered in the presence of a binder such as cobalt, nickel, or iron as well as alloys thereof. The term “diamond” refers to polycrystalline diamond, cubic boron nitride or wurtzite boron nitride and mixtures thereof.

SUMMARY OF THE INVENTION

[0011] The present invention overcomes the shortcomings associated with known rotatable cutting tools and teaches the construction and operation of an insert for road construction or mining attack tools. The present invention of a monolithic diamond tipped cemented carbide body segment, joined to the steel shank at a specified braze area ratio, serves to protect the diamond tip from base erosion and channels the flow of material away from the steel shank so as to significantly reduce premature washout wear and failure, which are the most common modes of failure with all diamond tipped previous inventions.

[0012] Since the coefficient of friction of tungsten carbide is substantially lower than that of steel, less heat is generated as the protective body of the present invention cuts through coal and rock thus increasing the safety of operation by reducing the potential of sparking and explosion from ignition.

DETAILED DESCRIPTION

[0013] Referring to the drawings more particularly by reference numbers wherein like numerals refer to like parts. FIG. 1 identifies a protective hard body constructed according to the teachings of the present invention. Shown in FIG. 2 is a preferred segmented embodiment of the invention of a rotatable cutter bit having a diamond coated cemented tungsten carbide tip 1, a cemented carbide body 2 and a steel body 3. The base of the carbide protective post 2 is joined to the steel shank 3 by a medium to high strength braze alloy. The head portion 2, and the shank 3 are coaxially aligned. The shank 3 having at its widest diameter, an enlarged section 4, which prevents the tool from being forced into the opening of the mounting block. The rearward steel member 3 may be seen to include a generally cylindrical shank portion 5 having an annular groove 6 near the rearward end and a frusto conical portion 7 adjacent forward to the shank portion 5. The frusto conical portion 7 has a continuously radiused socket 8 at its forward end.

[0014]FIG. 3 shows the present invention monolithic protective body segment 2, which includes a circular diamond tipped head end portion 1 and a continuously varying radiused tail end section 9 which is brazed into a continuously varying radiused socket 8 of the steel shank 3. The head end portion of 2, has an angular radiused frusto conical surface 10 leading away from the diamond tip 1 towards its widest diameter 11, which is centered about the longitudinal axis formed by varying radius B that leads down the length of the body to point 11, meeting a wider band 12, and a convex surface with a continuously varying radius 9, that serve to retain and strengthen the carbide body when brazed into the matching shank pocket 8 with a medium to high temperature braze.

[0015] The values of angle A of the diamond tip and, or the angle B, leading away from the diamond tip to the widest part of the carbide section, will vary depending on the particular mining application. For example, a range from 30 to 60 degrees has been found by the inventor to be the most effective range for the angle A, while a range from 5 to 15 degrees has been found to be most effective for angle B.

[0016]FIG. 4 shows the cemented carbide substrate portion of the monolithic body prior to affixing the diamond at the forward tip. The surface 13 serves as a substrate onto which the diamond is applied. The diamond is applied and covers the rounded tip surface 14, the nodular frusto conical retention surface containing one or more layers of rounded radiused protuberances 15, and the frusto conical planar surface 16 until it meets a step in the carbide substrate at a band 17. 

What I claim as my invention is:
 1. A rotatable cutting bit for impacting, fragmenting and removing material such as asphalt, concrete, rock, and minerals, the rotatable cutting bit comprised of: a polycrystalline diamond tip, affixed to a cemented carbide substrate by high temperature and pressure bonding, forming a monolithic unitary body, positioned at the forward central axis extremity of the cutter bit, having coaxially aligned, rotationally symmetric about its longitudinal axis, two monolithic integral sections, said sections comprising a tip section, and a base section, having a maximum diameter at said base section, and having a flat surface or a convex protrusion or continuously varying radiused extension at its rearward section. a ferrous body with a head section and elongated shank having a circular cross section, said body depending from said protective monolithic body along a longitudinal axis, said head portion having a flat surface or concave seat or continuously varying radiused socket at the forward end.
 2. The rotatable cutting tool of claim 1 wherein the forward monolithic section is coated with polycrystalline diamond, cubic boron nitride, wurtzite boron nitride or mixtures thereof formed by a method that comprises the placing within a reaction cell pre-pressed forms of abrasive particles affixed to the tip of the cemented carbide substrate and simultaneously subjecting the cell and the contents thereof to temperature and pressure conditions at which the diamond, cubic boron nitride or wurtzite boron nitride particles form a super hard abrasion resistant polycrystalline layer permanently sinter reaction bonded to the tip of the cemented carbide substrate.
 3. The rotatable cutting tool of claim 1 wherein the forward monolithic section has a cemented carbide substrate, which at its forward end has from 1-5 staggered concentrically layered rounded radiused protuberances that serve to support the diamond layer.
 4. The rotatable cutting tool of claim 1 wherein the forward end of the steel shank contains a flat surface or seat or continuously radiused socket defining a surface area, having an overall depth of 0.001 to 2.00 inches.
 5. The rotatable cutting tool of claim 1 wherein the axially rearward section of said monolithic insert has a flat surface or protruding or radiused extension that generally corresponds to, and fits into the shape of the flat surface or seat or continuously radiused socket of said steel shank.
 6. The rotatable cutting tool of claim 1 with a braze joint joining the surface area of the flat or protruding or radiused extension axially rearward section of said monolithic body to the flat surface, mating seat or radiused socket of the axially forward section of said ferrous shank by means of a medium to high impact resistant braze alloy.
 7. The brazed surface areas in claim 6 of said steel shank axially forward section flat surface, seat or radiused socket and said rearward monolithic protective body section flat surface, protruding or radiused extension to be at a ratio of steel shank surface area to monolithic body lateral cross sectioned area of 1.0 to 6.5.
 8. The rotatable cutting tool of claim 1 wherein the tip is made of a polycrystalline diamond affixed in situ to the carbide substrate by high temperature and high pressure.
 9. The rotatable cutting tool of claim 1 wherein the tip is made of a polycrystalline cubic boron nitride affixed in situ to the carbide substrate by high temperature and high pressure.
 10. The rotatable cutting tool of claim 1 wherein the monolithic cemented carbide section is made of a composition containing grains of carbide of group IVB, VB, or VIB metals pressed and sintered in the presence of a binder such as 5.0 to 18.0% cobalt, nickel, iron or alloys thereof.
 11. The rotatable cutting tool of claim 1 wherein the monolithic cemented carbide section is made of a composition containing carbide of group IVB, VB, or VIB metals having grain sizes from 0.01 to 30 microns as measured on a sintered, polished and etched part at 100 to 1500× optical magnification.
 12. The rotatable cutting tool of claim 1 wherein said monolithic protective cemented carbide section has a frusto conical surface or surfaces leading from the diamond tip or front of the body, to the rear of said body, where it is attached to the head of the ferrous shank; the resulting diameter at the rear of said protective body being larger, ranging 0.75 to 2.5 inches, than the diameter at the front of said protective body, ranging 0.25 to 1.5 inches.
 13. The rotatable cutting tool of claim 1 wherein said monolithic protective cemented carbide section has an overall length of 0.01 to 3.0 inches.
 14. The rotatable cutting tool of claim 1 wherein said monolithic protective cemented carbide section has a plurality of peripherally spaced, laterally projecting surfaces or vanes extending generally longitudinally along the bit, each surface or vane being substantially triangular with a narrow leading end and a wider trailing end, and having relatively diverging sides that extend from the leading end to the trailing end, the purpose of which is to effect a positive rotation of the bit upon contact with material being impacted, fragmented or removed.
 15. The rotatable cutting tool of claim 1 wherein said steel shank has a means for holding a loosely resilient retainer on the steel body that allows the cutter bit to rotate about its longitudinal axis in a mounting block. 